PNNL RIFT for Hurricane Laura 08252020

Simulation Information

• Forecast Date: 8/25/2020 12z – 90-m resolution run • Simulation Type: Rainfall-Runoff – 48 hrs precipitation (starting hour 25), 10 days total time.

Input Data Datasets

• Precipitation Data: 6-hr QPF 20200825 Hour 12Z forecast Times 30 through 72 (for hours 25 – 72). These data were converted to hourly rainfall using an equal distribution for each of the 6 hours of the forecast Topography Data: 90-m resolution (upscaled) DEMs for much of Louisiana. Levees, where available, were burned into the DEM. HUC4 boundaries, intersected with forecasted precipitation, were used to constrain the simulation domain. HUC4s included 0808, 0804, 1114, 1201/1202, and the eastern portion of 1204 which includes Port Arthur. The "/" indicates HUCs that were run as a single simulation. • Simulation Timeframe: 48 hours of precipitation were used, and the simulation was run for 10 days.

Simulation-Specific Caveats

• Storm surge impacts are not included. • New Orleans is a unique hydrologic region with a strong dependence on floodwater removal infrastructure (pumps). These removal processes are not currently accounted for in RIFT and flooded areas in these locations should be used cautiously especially in regions with low depths. • The current scenarios can be a considered a worst-case scenario where floodwater removal infrastructure is inoperable. • The 0808, 1114, and 0804 HUCs were run independently. This means that cross-basin fluxes are ignored. This is reasonable given the storm track and areas of intense precipitation to the west and upstream end of HUCs 1114 and 0804, and therefore not expected to influence downstream peak flood extents.